Vitamins are an important and expensive part of a cow's ration. So, it's important that we try to preserve the vitamins that we harvest in our forages and curb the losses of the vitamins that we purchase.
Vitamins in forages are very unstable – easily destroyed during maturation, harvest and storage.
- Carotene (the precursor of vitamin A) decreases after the bloom stage. Much of the carotene is lost during field curing, especially when rained on. Heating in the bale or silo further reduces vitamin A activity. Forage will lose up to 60% of its vitamin A activity in the first six months of storage.
- Vitamin E is very susceptible to heat, moisture and oxidation during harvest and storage. Ensiling also destroys most of the vitamin E activity in high moisture grains.
- Sun curing of forages increases vitamin D content, but leaf losses will reduce vitamin D. Covering stored hay and silage will reduce vitamin losses as will proper baling and ensiling procedures that prevent excessive heating. Green chopping or grazing fresh forages is an excellent way to provide vitamins, especially A and E.
You may have noticed that your purchased vitamin costs have increased dramatically. This has been due to the loss of domestic production and demand pressure from world markets. So we should be aware of what causes losses in vitamin activity of supplements too. Vitamins are manufactured with protective coatings and various means of chemical stabilization to reduce destruction of vitamin activity. But, commercial vitamins are also susceptible to heat, humidity, oxidation and abrasion during processing and storage.
Pelleting and extrusion of feeds can destroy vitamins through friction and pressure. Trace minerals also affect vitamins. Oxidation and reduction reactions caused by trace minerals, especially sulfates, destroy vitamins. Abrasion from trace minerals destroys the protective coating of some vitamins.
Losses of vitamin A and E and niacin average about 5 – 8% per month in vitamin/trace mineral (VTM) premixes. For this reason, VTM premixes should be purchased in quantities that keep inventories rotated regularly.
Premixes should be used within about 3 months. A feed manufacturer may buy a VTM premix from a premix manufacturer, who in turn buys from a distributor, who buys from the vitamin manufacturer. So the time between the manufacture and feeding of vitamins is potentially quite long. With high vitamin prices, make sure you're getting what you pay for and preserving what you have on the farm.
--Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. You can contact him at firstname.lastname@example.org.
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